My two cents as a person who has had issues with oxers as well, my two main problems have been:
1. you guessed it, catching them in the mouth because I'm not talented at jumping, and get thrown off balance.
2. LACK OF CONFIDENCE...if you're scared of that oxer, your horse knows it. You need to build up slow and you need to really convince that horse that you WANT to go over it. make sure you aren't looking down and make sure you don't have an ounce of hesitation in your body(or mind)
....I'm still working on that second one! haha good luck!
A horse is the projection of peoples' views about themselves--strong, powerful, beautiful--and it has the capability of giving us escape from our mundane existance.